. Give chemical tests to distinguish between compounds in the following pairs of substances


(a) Give chemical tests to distinguish between compounds in the following pairs of substances:

(i) Ethanal and Propanal

(ii) Benzoic acid and Ethyl benzoate

(b) An organic compound contains 69.77% carbon, 11.63% hydrogen and rest oxygen. The molecular mass of the compound is 86. It does not reduce Tollen’s reagent           but forms an addition compound with sodium hydrogensulphite and gives positive iodoform test. On vigorous addition, it gives ethanoic and propanoic acids. Derive         the structure of the compound ‘A’

                                                                                              OR

(a) Arrange the following compounds in an increasing order of their indicated property:

     (i) Benzoic acid, 4-Nitrobenzoic acid, 3,4-Dinitrobenzoic acid, 4-Methoxybenzoic acid (acid strength)

     (ii) CH3CH2CH(Br)COOH, CH3CH(Br) CH2COOH,

          (CH3 )2CHCOOH, CH3CH2CH2COOH (acid strength)

(b) How would you bring about the following conversions:

   (i) Propanone to Propene

   (ii) Benzoic acid to Benzaldehyde

   (iii) Bromobenzene to 1-phenylethanol

Best Answer

(i) Ethanol, when warmed with NaOI (I2 /NaOH) gives yellow ppt of Iodoform while propanal does not

    Ethanol

(ii) Benzoic acid being an acid, decomposes NaHCO3 to produce brisk effervescence due to evolution of CO2 while ethyl benzoate does not

      Benzoic acid

Empirical formula

As the compound A forms addition compound with NaHSO3 therefore it must be either an aldehyde or ketone

As it does not reduce Tollens reagent and give positive Iodoform test therefore it must be a methyl ketone

As on oxidation the compound A gives a mixture of ethanoic acid and propanoic acid, therefore compound A is

        The chemical reactions are

          Bromobenzene

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